GBU-31 3D model not correct.

[Capn kamikaze]

I noticed that the GUB-31 model has one of the fins as a fixed surface, with three moveable fins.

This is incorrect, the only ones that have fixed fins are the training bombs, and all of those are fixed not just one.

If the real one had one fixed fin it would immediately start spinning about the long axis of the bomb if that fin deflected.

I think I know why this has happened, there's an old 3d cut away drawing of an aircraft with weapons out there, can't remember exactly where, but it shows one as being fixed, I think this drawing may be the source of the error.

This stuck in my mind as I asked about this drawing on another forum years ago, and was told that it was incorrect, so perhaps someone has used this incorrect drawing as the basis for the 3D model?

[Tholozor]

From documentation I've read and diagrams I've seen, the fixed fin is correct. The bomb should orient itself so that the fixed fin is in the ventral position, with the adjacent control fins acting as elevators, and the opposing control fin acting as a rudder (AFAIK, the reorientation post-release only applies to the GBU-31(V)2/B, with other variants of the -31 flying canted). The fins should have locking pins that hold them in place while in carriage, and disengaged when released.

I've also noticed that the models for all JDAMs don't even have animations for the control fins moving, so it'll look like all fins are fixed throughout the flight.

Edited August 6, 2023 by Tholozor

[Capn kamikaze]

7 hours ago, Tholozor said:

From documentation I've read and diagrams I've seen, the fixed fin is correct. The bomb should orient itself so that the fixed fin is in the ventral position, with the adjacent control fins acting as elevators, and the opposing control fin acting as a rudder (AFAIK, the reorientation post-release only applies to the GBU-31(V)2/B, with other variants of the -31 flying canted). The fins should have locking pins that hold them in place while in carriage, and disengaged when released.

I've also noticed that the models for all JDAMs don't even have animations for the control fins moving, so it'll look like all fins are fixed throughout the flight.

 

The photos I am seeing look like they're all moveable, so far I've only seen fixed welded ones on photos of inert bombs, and they are all the fins.

https://www.everycrsreport.com/files/20200227_R45996_efe24af9217806533af112447842e2bb9ccf5b17.html#_Toc33692032

And...

The guidance section can't be fitted in just any orientation, note that rectangular part on the top.

Edited August 6, 2023 by Capn kamikaze